Parasitology Flashcards
Stomoxys calcitrans is known by which other name?
Stable fly
Which flies cause sweet itch in horses?
Culicoides
How long is the cyathostomin life cycle?
6-8 weeks
The classification of strongyles into ‘large’ or ‘small’ depends on the size of what?
The mouthpiece
What is meant by the prepatent stage?
The time between picking up larvae and passing out eggs in faeces
In the cyathostomin life cycle, which larvae stage is ingested by the horse?
L3
In the cyathostomin life cycle, stahe L2 has a protective sheath, but where is it lost?
Small intestine of the horse
In which stage of the cyathostomin life cycle would you expect a horse to show clinical signs?
EL3
What are the clinical signs of cyathostomins?
Oedema Diarrhoea Colic Weight loss 50% mortality Often seen in naive young animals
What is meant by hypobiosis?
Inhibited larval development within the host
In the cyathostomin life cycle, when is the highest shedding of eggs?
August
In the cyathostomin life cycle, when is there a peak of L3 on pasture?
Late summer (August/September)
Name 4 anthelmintics used to treat cyathostomins?
Ivermectin
Moxidectin
Benzimidazoles
Pyrantel
How is the type of disease (acute, sub-acute or chronic) determined with fasciola hepatica?
Determined by number of metacercariae ingested and the time period over which they were ingested
How could you identify acute fasciolosis in the liver of an affected sheep?
Visible multifocal necrotic or haemorrhagic tracts can be seen throughout the liver (of migrating juvenile flukes)
What are the clinical signs of acute fasciolosis?
What animal does it typically affect?
When does it occur?
Sheep
Sudden death, weakness/dullness, abdominal pain, anaemia
Juvenile flukes migrating through liver parenchyma causes multifocal necrotic or haemorrhagic tracts
October-January
What are the clinical signs of sub-acute fasciolosis?
How is it caused?
Rapid weight loss, anaemia
Sheep ingest metacercariae over a longer period of time
What are the clinical signs of chronic fasciolosis?
Which animals does it affect?
How does it happen?
When does disease occur?
Progressive weight loss, anaemia, sub-mandibular oedema, ascites
Sheep and cattle
Low numbers of metacercariae ingested over a longer period of time
Disease in late winter/early spring: Jan/March
Name 3 ways you can diagnose a fluke infection?
Faecal egg counts Post-mortem Clinical signs Copro-antigen ELISA Antibody detection ELISA
Which drug is typically used to treat fluke?
Triclabendazole
Name the 3 classes of anthelmintics, and name a drug from each class
- Benzimidazoles- Panacur (fenbendazole), triclabendazole
- Imidathiazoles/ tetrahydroprimidines- levamisole, Pyrantel
- Macrocyclic lactones- avermectins eg ivermectin, milbemycins eg Moxidectin
Which animals are the primary source of toxiplasma gondii infection in sheep?
Cats shed oocysts in pastures
What is meant by refugia?
The proportion of a parasite population that is not selected by drug treatment (in refuge from a drug)
What is a parasite?
An organism that is dependent metabolically on another, where that organism benefits at the expense of the other
An arthropod is classed as an invertebrate animal having what?
An external waterproof skeleton which is mainly made of a-chitin
A segmented body
Jointed limbs
A haemocoel-the body cavity which contains haemolymph (blood)
What is the name of the system which filters waste from the haemolymph into the gut in arthropods (insects and arachnids)?
Malpighian tubules
What are the two types of arthropod life cycle?
Holometabolous-complete metamorphosis eg flies
Hemimetabolous-incomplete metamorphosis eg ticks and lice
Which macrocyclic lactone has a zero milk withdrawal period?
Eprinomectin
Which areas of a horses body are affected by sweet itch?
Self-inflicted lesions on the withers, mane, tail, face
Culicoides are vectors of which viruses?
Bluetongue (cattle, sheep) Schmallenberg (calves and lambs) Epizootic Haemorrhagic Fever (deer and livestock) Bovine Ephemeral fever (cattle) Transmit African Horse Sickness
Which word is given to the process where fly larvae invades and feeds on living or necrotic tissue?
Myiasis
How long is the life cycle of Culicoides (biting midges)?
Eggs to adults in 3 weeks, can be less in warmer climates
What are the clinical signs of sweet itch in horses?
Pruritic dermatitis
Self-inflicted lesions on withers, mane, tail, face
Hair loss, excoriation, crusting and scaling, eventually hyperkeratosis and thickening
Which parasite transmits leishmaniasis in dogs?
Sandflies
Which are the 2 main genera of Tabanidae?
Tabanus and Haematopota
Which anthelmintics would you use to treat Gasterophilus spp?
Ivermectin or moxidectin
What are the 3 species of Gasterophilus?
G. intestinalis
G. nasalis
G. haemorrhoidalis
How long is the Chorioptes life cycle? (horse mite)
3 weeks
What are the two sub-orders of lice?
Anoplura- blood-sucking
Mallophaga- biting/chewing (feed on skin/scales etc)
Which is the most widespread species of flea?
Cat flea (Ctenocephalides felis)
What is the purpose of ctenidia on fleas?
Enable them to stand up between hairs (would otherwise wobble and fall)
Describe the flea life cycle
- Adults live permanently on host
- Females start laying eggs within 48 hours of infestation, and can lay 40-50 eggs per day. Eggs fall off host
- Larvae (3 stages) develop in the environment
- Metamorphosis from larvae to adult via pupae. In the cocoon, pre-emerged adults can wait up to 6 months for a suitable host
Whole cycle can take as little as 3 weeks
What are the clinical signs of FAD?
Alopecia, excessive grooming, skin damage
Fleas and lice (Trichodectes canis) can be intermediate hosts of what?
Dipylidium caninum (tapeworm)
Give an ideal flea control program
Adulticide eg Fipronil (Frontline)
Insect growth regulator eg Lufenuron
Juvenile hormone analogue eg Methoprene
Describe the Trichodectes canis (biting/chewing louse) life cycle
- Adult biting lice live permanently on host
- Females lay individual eggs (nits) and attach them to hair shafts
- All 3 nymph stages develop on the host
Full cycle takes place on host and is completed in 4-6 weeks
What does ELISA stand for and what does it do?
Enzyme-linked immunosorbent assay
Uses antibodies and colour change to identify a substance
What does the Demodex life cycle consist of?
Eggs, 2 larval stages, 2 nymphal stages, adult
Takes 18-24 days
Which mange mite causes ‘walking dandruff’?
Chyletiella spp
Give an example of a synthetic pyrethroid?
Flumethrin
What are the differences between trematodes (flukes) and cestodes (tapeworms)?
Flukes are free-living, whereas tapeworms are always parasitic
Flukes are dorso-ventrally flattened, tapeworms are ribbon-like and segmented
Flukes are mainly hermaphrodite, tapeworms are always hermaphrodite
Both have no body cavity
Flukes have a gut but no anus, tapeworms have no gut
What is the infective stage in the strongyle life cycle?
iL3
Give a common anthelmintic drug combination for: Horses Cattle Sheep Dogs and cats
Horses: moxidectin and praziquantel
Cattle: ivermectin and triclabendazole
Sheep: levamisole and triclabendazole
Dogs and cats: pyrantel and praziquantel
What is the difference between interval, strategic and targeted dosing of anthelmintics?
Interval dosing: treat at regular intervals based on egg reappearance period
Strategic dosing: treat when parasite number is highest to disrupt seasonal cycle of transmission
Targeted dosing: treat on the basis of diagnostic indicators
Describe the life cycle of toxoplasma gondii
- Cats=definitive host. Infected by ingesting bradyzoite cysts in tissues of prey
- Sexual cycle in SI. Oocysts shed in faeces.
- Oocysts sporulate and contaminate environment, food, water. Eaten by any warm-blooded animal. A sporulated oocyst contains 2 sporocysts, each containing 4 sporozoites.
- In intermediate host (rodents, birds), sporozoites are released. They cross the gut wall and develop to tachyzoites. These replicate rapidly then differentiate to bradyzoites before forming cysts.
What is the difference between holometabolous and hemimetabolous arthropods?
Holometabolous: complete metamorphosis eg flies
Hemimetabolous: imcomplete metamorphosis eg lice and ticks
How do organophosphates work?
Inhibit acetylcholinesterase by mimicking the structure of Ach
Leads to accumulated neurotransmitter -> paralysis
How do synthetic pyrethroids work?
Excite and depolarise cell membranes ->paralysis
How do macrocyclic lactones work?
Stimulate GABA release and enhance binding -> increased flow of Cl- into cells -> hyperpolarization -> flaccid paralysis
How do insect growth regulators work?
Inhibit chitin synthesis or mimic native hormones
What is meant by ‘gadding’ in horses, and to a lesser extent cattle?
Restlessness and excitement caused by the presence of biting flies (particularly warble flied in cattle and bots in horses)
Which species of fly causes ‘gadding’ in horses, are active during sunny days and transmit trypanosomes and equine infectious anaemia?
Tabanids
Which fly species has a life cycle as little as 3 weeks, lays eggs in damp marshy land, and has mottled brown wings laid flat over its body?
Culicoides
Which fly species has a 4 week life cycle and always lays eggs in running water, with the adults being active in the morning and evening?
Also transmit Onchocerca spp
Blackflies (Simulium spp)
Which fly species prefers to feed on the lower parts of the animal, have very long mouthparts, rest on sun-exposed gates etc, live inside barns, lay eggs on dung mixed with straw, and are vectors of BVD, anthrax and EIA?
Stomoxys calcitrans (stable fly)
Hydrotaea irritans (‘the headfly’), Musca autumnalis (‘the face fly’), and Musca domestica (‘the housefly’) are all what?
Non-biting muscidae
Which fly species lays eggs on dung at pasture, doesn’t enter housing buildings, congregates around corners of eye/teats (causing ‘summer mastitis’), and is most numerous on warm, humid, overcast days in August?
Hydrotaea irritans (headfly)
Which fly species lays eggs on dung at pasture, usually in early summer, is brown/grey in colour and causes Pink eye/New Forest eye in cattle?
Musca autumnalis (‘facefly’)
Describe the life cycle of G. intestinalis
Lay eggs on inner forelegs, burrow in tongue, moult and exit to pharynx (takes 3-4 weeks), moult to L2, cluster in oesophageal portion of stomach.
Moult to L3 and remain until following spring; passed in dung around June.
Larvae have a double row of spines.
Which mite species has unjointed pedicels ending in a cup-shaped sucker?
Chorioptes
When does chorioptic mange occur?
How is it caused?
Winter disease
Caused by chewing rather than skin-piercing activity
What is the life cycle of the chorioptes mite?
6-legged larva hatches from egg -> feeding -> moulting -> 8-legged protonymph -> tritonymph -> adult
3 weeks long
Females may produce up to 20 eggs
What causes sheep scab?
Psoroptes ovis
Which mite species has 3-jointed pedicels with trumpet-shaped suckers?
Psoroptes
Of anoplura and mallophaga (lice sub-orders), which are found on birds/mammals/both?
Anoplura: mammals
Mallophaga: mammals and birds
Which drugs can be used against horse flies and lice?
Permethrin and Cypermethrin
What are the general features of lice?
Host-specific (often site-specific)
All stages on host, die within days if off host
A host in a good state of health manages to remove most of its lice from the body (indicative of neglect)
Large numbers of lice cause irritation, inflammation, pruritis, dermatitis, reduced weight-gain
Small wingless insects, flattened stout legs and claws for clinging tightly to hair/fur/feathers
How does fipronil work?
Interacts with ligand-gated Cl- channels (particularly GABA), blocking pre- and post-synaptic transfer of Cl- ions across cell membranes.
Uncontrolled CNS activity -> death
Kills fleas within 24 hours and lice within 48 hours
What is the life cycle of sarcoptes scabiei?
Females create winding tunnels parallel to the skin surface, feeding on fluid between the cells
Each tunnel (1-2cm in length, just below the skin) contains a single female mite-lays 3 eggs a day
Hatch to larvae within the tunnels after 3-4 days
Larvae exit the tunnels, successive moulting to 8-legged protonymph -> tritonymph -> adult
Egg to adult cycle= 14 days
Why might diagnosis of sarcoptes scabiei require several deep skin scrapings?
Females live in winding tunnels 1-2cm below the skin surface
Which drugs can you use to treat sarcoptes scabiei (mange mite)?
Amitraz, selamectin (not ivermectin- CI in dogs)
Which mite species is commensal in dogs?
Demodex
What drugs can be used to treat demodex?
Amitraz, imidacloprid/moxidectin
How long is the life cycle of ixodes ricinus? (tick)
How many hosts do they have?
3 years
3 hosts
Which tick species has an anal groove?
Ixodes ricinus
What is babesiosus transmitted by?
Ticks
Which drugs can be used against ticks in cattle?
Organophosphates, pyrethroids, amitraz
Which type of drug can be administered as pour ons, ear-tags and sprays in cattle against pasture flies eg Hydrotaea irritans?
Synthetic pyrethroids
Which drugs can you use to treat lice in cattle?
Synthetic pyrethroids, macrocyclic lactones
Why might a drug fail?
An inadequate dose of drug was administered
Activity of the drug is reduced
Parasite species/stage present were not susceptible to drug
Errors in methods used for FEC or interpretation of results
How is sheep scab transmitted (psoroptes ovis)?
Sheep to sheep
Fomites (infected trailers, fencing)
Contaminated environment (can survive off host for 14-16 days)
Introduced to a flock by new untreated sheep, using rented land, poor fencing (infested strays)
In which season is sheep scab most common?
Winter
How can you control/prevent sheep scab?
Dipping (OP)
Injectable ivermectin, moxidectin
What is meant by myiasis?
The infestation of the organs and tissues of living animals by the larvae of dipteran flies
What are keds?
How is transmission achieved?
What do they do?
Wingless flies
Sheep-to-sheep
Suck blood, cause pruritis, loss of condition
Mainly a problem in winter
When would you give a cow ear tags containing pyrethroids (for which flies)?
Nuisance/biting flies
